This invention relates to novel compounds that are infrared radiation sensitive. More particularly, this invention relates to novel oxonol compounds that are sensitive at 700 nm or higher wavelengths in water or water-miscible organic solvents.
Particulate compounds that absorb at various wavelengths have been used in photographic silver halide materials for many years. For example, such compounds have been used as xe2x80x9cfilterxe2x80x9d dyes to absorb electromagnetic radiation (xe2x80x9clightxe2x80x9d) from different regions of the electromagnetic spectrum, such as red, blue, green, ultraviolet and infrared regions. These filter dyes are often required to perform the function of absorbing light during exposure of the material so as to prevent or at least inhibit light of a particular region of the spectrum from reaching at least one of the radiation-sensitive layers of the material.
Particulate filter dyes can be designed with various features to facilitate their use and/or immobilization in photographic materials, as described for example in U.S. Pat. No. 5,213,956 (Diehl et al.).
There is a need in the photographic industry for compounds that absorb in the near infrared and infrared regions of the electromagnetic spectrum for various purposes. Such materials can be used, for example, to absorb heat and to initiate or facilitate imaging in lithographic printing plates. However, such compounds (that is, IR dye sensitizers) must be compatible with other components of imaging formulations used in such printing plates.
Organic dye salts, by nature, are often partially soluble in water or alcoholic coating solvents and are thus preferred as IR dye sensitizers in lithographic plate imaging compositions. However, many such salts have been found to be unacceptable because of insufficient solubility, because they react with the charged polymer to form hydrophobic products that can result in scummed or toned images, or because they offer insufficient thermal sensitization in imaging members. In particular, there is a need to have IR dye sensitizers that are compatible with thiosulfate polymers, such as those described in U.S. Pat. No. 5,985,514 (Zheng et al.).
Useful oxonol IR-sensitive compounds with various heterocyclic and carbocyclic moieties are described in U.S. Pat. No. 6,248,886 (Williams et al.) and U.S. Pat. No. 6,248,893 (Williams et al.).
There is a continuing need for IR-sensitive compounds for various imaging applications.
We have discovered that certain oxonol compounds are useful as infrared radiation absorbing compounds in printing plates and other thermally-sensitive imaging materials. These novel compounds are soluble in water or water-miscible organic solvents, absorb radiation and have a xcexmax greater than 700 nm as measured in water or a water-miscible organic solvent. These compounds are also represented by Structure DYE shown as follows: 
wherein R is a substituted or unsubstituted alkyl group, substituted or unsubstituted cycloalkyl group, or substituted or unsubstituted heterocyclic group, or a substituted or unsubstituted carbocyclic aromatic group, R1 and R2 are independently substituted or unsubstituted heterocyclic or carbocyclic aromatic groups, and M+ is a monovalent cation.
These compounds have been found not only to have the desired infrared radiation absorption characteristics but also to be soluble in water or water-miscible organic solvents that are often used to formulate and coat lithographic printing plate imaging compositions. In addition, these compounds are compatible with negatively or positively charged polymers that may be present in those compositions (for example, anionic polymers used for imaging such as those described in U.S. Pat. No. 5,985,514, noted above). In other words, no precipitates are formed when such compounds and polymers are mixed.
A preferred use of the compounds of this invention is described in copending and commonly assigned U.S. Ser. No. 09/947,112, filed on even date herewith by Zheng et al. and entitled xe2x80x9cThermal Switchable Composition And Imaging Member Containing Complex Oxonol IR Dye And Methods Of Imaging And Printingxe2x80x9d.
The compounds can also be used as filter dyes that are compatible with components in color and black-and-white photographic silver halide layers and that do not adversely affect the sensitometric properties of such layers.